The present invention relates to an ultrasonic imaging apparatus capable of displaying B- and Doppler-mode images.
Ultrasonic imaging apparatuses are widely used in various industrial fields. In particular, development of ultrasonic imaging apparatuses as ultrasonic diagnostic apparatuses has been significant in the medical field. A recent ultrasonic diagnostic apparatus can display both a tomographic image (i.e., a B-mode image) and a blood flow image (i.e., a Doppler-mode image). Such a conventional ultrasonic diagnostic apparatus is used for cardiac or carotid diagnosis. Therefore, both a tomographic image of a portion to be examined, and a blood flow state of the blood vessel system shown in the tomographic image can be displayed.
There are two types of conventional ultrasonic imaging apparatus capable of displaying the mode images described above. The first apparatus has a B-mode ultrasonic probe and a Doppler mode single probe in an acoustic medium. In this apparatus, the B-mode ultrasonic probe is driven by a 7.5- or 10-MHz RF drive signal to acquire high -resolution B-mode image data. The Doppler mode single probe is driven by a 3.5-MHz low frequency signal and outputs a Doppler signal for measuring a blood flow speed.
The second apparatus uses an electronic linear ultrasonic probe. Electronic scanning is performed to obtain a B-mode image, and an ultrasonic beam is obliquely emitted to obtain a Doppler mode image.
The first conventional ultrasonic imaging apparatus requires two types of probes thus complicating the overall structure of the probe, thereby degrading reliability and posing maintenance problems. The second conventional ultrasonic imaging apparatus is driven at an identical frequency in the B and Doppler modes. Therefore, the B- and Doppler-mode images having opposite frequency characteristics cannot be produced in an optimal state. More specifically, the resolution of the B-mode image can be improved at high drive frequencies. However, the Doppler signal is greatly attenuated at high drive frequencies, and a good Doppler-mode image cannot be obtained. Also, as the Doppler shift is proportional to the blood flow speed, a detectable highest flow speed is limited.